Segment Information (Revenues By Geographic Location) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 908,356	$ 841,251	$ 842,980	$ 825,678	$ 904,763	$ 813,270	$ 796,759	$ 760,802	$ 3,418,265	$ 3,275,594	$ 3,142,856
Enterprise and Service Provider
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									2,736,080	2,646,154	2,563,064
GoTo Business Division
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									682,185	629,440	579,792
Operating Segments | Enterprise and Service Provider
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									2,736,080	2,646,154	2,563,064
Operating Segments | Enterprise and Service Provider | Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									1,598,896	1,487,364	1,394,112
Operating Segments | Enterprise and Service Provider | EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									863,517	873,620	863,179
Operating Segments | Enterprise and Service Provider | Asia-Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									273,667	285,170	305,773
Operating Segments | GoTo Business Division
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									682,185	629,440	579,792
Operating Segments | GoTo Business Division | Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									574,882	524,520	475,884
Operating Segments | GoTo Business Division | EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									87,331	84,481	83,930
Operating Segments | GoTo Business Division | Asia-Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									$ 19,972	$ 20,439	$ 19,978